Heat exchangers

ABSTRACT

Provided herein are air-to-air heat exchangers. In some embodiments, the air-to-air heat exchanger comprises at least one first air passageway extending between a first air inlet and a first air outlet; at least one second air passageway extending between a second air inlet and a second air outlet; at least one heat-conductive wall separating the at least one first air passageway from the at least one second air passageway; and at least one electrohydrodynamic device disposed in at least one of the first and second air passageways for enhancing airflow therein. Also provided herein is a method of using electrohydrodynamic devices to enhance airflow and efficiency of air-to-air heat exchangers.

BACKGROUND OF THE DISCLOSURE

There is a need for energy-efficient air-to-air heat exchangers andmethods that provides efficient heat exchange between airflows dividedby one or more separation walls.

SUMMARY OF THE DISCLOSURE

Provided herein are air-to-air heat exchangers that areelectrohydrodynamically enhanced. In some embodiments, the air to airheat exchanger comprises at least one first air passageway extendingbetween a first air inlet and a first air outlet; at least one secondair passageway extending between a second air inlet and a second airoutlet; at least one heat-conductive wall separating the at least onefirst air passageway from the at least one second air passageway; and atleast one electrohydrodynamic device disposed in at least one of thefirst and second air passageways for enhancing airflow therein.

In some embodiments, the at least one heat conductive wall comprises atleast one essentially planar wall. In some embodiments, the at least oneheat conductive wall comprises a plurality of essentially planar wallsthat are essentially parallel to one another. In some embodiments, theplurality of heat conductive walls are essentially equidistantlyarranged.

In some embodiments, airflow in the first air passageway and airflow inthe second air passageway are essentially in opposite direction.

In some embodiments, each electrohydrodynamic device comprises one ormore emitter electrodes, one or more enhancer electrodes positioneddownstream of the one or more emitter electrodes, and one or morecollector electrodes positioned downstream of the one or more enhancerelectrode. In some embodiments, the one or more emitter electrodes, theone or more enhancer electrodes, and the one or more collectorelectrodes extend essentially parallel to the heat conductive walls andessentially orthogonal to the airflow.

In some embodiments, the one or more emitter electrodes have a higherelectric potential than the one or more enhancer electrodes, and the oneor more enhancer electrodes have a higher electric potential that theone or more enhancer electrodes. In some embodiments, the one or moreenhancer electrodes are grounded.

In some embodiments, the one or more enhancer electrodes are positionedcloser to the one or more emitter electrode than to the one or morecollector electrodes.

In some embodiments, the one or more emitter electrodes are separatedfrom the closest heat conductive wall by an emitter-wall distance.

In some embodiments, the one or more enhancer electrodes and the one ormore collector electrodes are attached to the heat conductive wall, andthe heat conductive wall is dielectric. In some embodiments, the one ormore enhancer electrodes and the one or more collector electrodes aremade of heat conductive material.

In some embodiments, the heat conductive wall is electrically conductiveand grounded, the one or more enhancer electrodes are separated from theclosest heat conductive wall by an enhancer-wall distance, and whereinthe one or more collector electrodes are separated from the closest heatconductive wall by a collector-wall distance.

In some embodiments, the collector-wall distance is smaller than theenhancer-wall distance. In some embodiments, the collector-wall distanceand the enhancer-wall distance are both smaller than the emitter-walldistance.

In some embodiments, each electrohydrodynamic device further comprisesone or more arrays of convection promoter electrodes positioneddownstream of the one or more collector electrodes. In some embodiments,the one or more arrays of convection promoter electrodes extendessentially parallel to the heat conductive walls and essentiallyorthogonal to the airflow.

In some embodiments, the convection promoter electrodes are separatedfrom the closest heat conductive wall by a promoter-wall distance of (h)that is smaller than any of the emitter-wall distance, enhancer-walldistance, and collector-wall distance. In some embodiments, theconvection promoter electrodes within each array are separated from oneanother by a promoter-promoter distance (s) that is greater than thepromoter-wall distance (h).

In some embodiments, each electrohydrodynamic device comprises two arrayof the convection promoter electrodes positioned between two adjacentheat conductive walls, wherein both arrays and have same electricalpotential.

In some embodiments, one array of convection promoter electrodes of afirst electrohydrodynamic device and one array of convection promoterelectrodes of a second electrohydrodynamic device are disposed onopposite side of a heat conductive wall with an offset distance (u), andhave opposite electric potentials.

In some embodiments, the promoter-promoter distance (s) is no less than2h+u, and wherein the promoter-promoter distance (s) is no greater thanX(2h+u), wherein X ranges between 1.5 and 2.0.

In some embodiments, the at least one first air passageway, the at leastone second air passageway, the at least one heat-conductive wall, andthe at least one electrohydrodynamic device are enclosed in a housing.In some embodiments, the housing comprises the first air inlet, thefirst air outlet, the second air inlet, and the second air outlet.

In some embodiments, the first air inlet is configured to receive airfrom atmosphere, and the first air outlet is connected to a desiccatorof a ventilation system. In some embodiments, the second air inlet isconfigured to receive exhaust air from the ventilation system, andwherein the second air outlet is configured to release air intoatmosphere. In some embodiments, a temperature of air entering into thefirst air inlet is higher than a temperature of air exiting the secondair outlet.

Also provided herein is a method of electrohydrodynamically enhancing inair-to-air heat exchangers. In some embodiments, the method comprisesactivating at least one electrohydrodynamic device disposed in airpassageways of the air-to-air heat exchanger. Each electrohydrodynamicdevice comprises one or more emitter electrodes, one or more enhancerelectrodes positioned downstream of the one or more emitter electrodes,and one or more collector electrodes positioned downstream of the one ormore enhancer electrodes. The activation comprises creating gradientelectric potential differential from the emitter electrodes to theenhancer electrodes and to the collector electrodes.

In some embodiments, the activation comprises coupling the emitterelectrodes with a source of positive electric potential, coupling thecollector electrode with a source of negative electric potential, andgrounding the enhancer electrodes.

Other features and technical effects of the present disclosure willbecome apparent from the following detailed description. It should beunderstood, however, that the detailed description and the specificexamples, while indicating specific embodiments, are given by way ofillustration only.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the disclosed air-to-air heat exchangers and method ofelectrohydrodynamically enhancing in air-to-air heat exchangers are setforth with particularity in the appended claims. A better understandingof the features of the present disclosure will be obtained by referenceto the following detailed description that sets forth illustrativeembodiments, in which the principles of the present disclosure areutilized, and the accompanying drawings of which:

FIG. 1A-1C graphically illustrate configurations of heat exchangerssuitable for use in the present disclosure: pipe-based (1A), cell-based(1B), and plate-based (1C);

FIG. 2A-2B graphically illustrate general concept of an ionic windgenerator (2A) and a cross-sectional view of a two-stage EHD device(2B), with the schematic diagram in 2A illustrating gas velocityprofiles before and after electrohydrodynamic enhancement;

FIG. 3 graphically illustrates configuration of an ionic wind generatorwith the enhancer electrode;

FIG. 4A-4B schematically illustrate ionic wind generators with enhancerelectrodes embedded into dielectric rectangular duct with one (4A) andtwo (4B) emitter electrode of corona discharge in the form of elongatedmembers. Thin lines denote electrical couplings. The case of positivecorona is illustrated as a non-limiting example;

FIG. 5 schematically illustrates configuration of ionic wind generatorembedded in a pipe-based heat exchanger. Thin lines denote electricalcouplings;

FIG. 6 schematically illustrates the arrangement of a plurality of ionicwind generators of the preferred configuration embedded into plate-basedheat exchanger with electrically non-conductive plates. Electricalcouplings are not shown. The case of positive corona sign is provided asa non-limiting example;

FIG. 7A-7B schematically illustrate configurations of ionic generatorsof bulk air wind embedded between the neighboring conductive plates ofplate-based heat exchanger in the cross-section view with one emitterelectrode (7A) and two emitter electrodes (7B) of the assisted coronadischarge. Emitter electrodes are in the form of elongated members,enhancer and collector electrodes are in the form of elongated membersas a non-limiting example;

FIG. 8 schematically illustrates the arrangement of a plurality ofshort-range ionic wind generators of the preferred configurationembedded into plate-based heat exchanger with electrically conductiveplates. Electrical couplings are not shown; and

FIG. 9 schematically illustrate the arrangement of a plurality of ionicgenerators of bulk air flow with alternating signs of corona dischargeand a plurality of series of short-range ion wind generators embeddedinto plate-based heat exchanger with electrically conductive plates.Ionic wind generators of bulk air flow which configurations are given inFIG. 9 are simply denoted with the sign of (emitter electrode) of coronadischarge. Electrical couplings are not shown.

It should be understood that the drawings are not necessarily to scaleand that the disclosed embodiments are sometimes illustrateddiagrammatically and in partial views. In certain instances, detailswhich are not necessary for an understanding of the disclosed device ormethod which render other details difficult to perceive may have beenomitted. It should be understood, of course, that this disclosure is notlimited to the particular embodiments illustrated herein.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure is described in greater detail below. Thisdescription is not intended to be a detailed catalog of all thedifferent ways in which the present disclosure may be implemented, orall the features that may be added to the present disclosure. Forexample, features illustrated with respect to one embodiment may beincorporated into other embodiments, and features illustrated withrespect to a particular embodiment may be deleted from that embodiment.In addition, numerous variations and additions to the variousembodiments suggested herein will be apparent to those skilled in theart in light of the instant disclosure, which do not depart from thepresent disclosure. Hence, the following specification is intended toillustrate some particular embodiments of the present disclosure, andnot to exhaustively specify all permutations, combinations andvariations thereof.

CERTAIN TERMINOLOGY

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as is commonly understood by one of skill in theart to which the claimed subject matter belongs. It is to be understoodthat the foregoing general description and the following detaileddescription are exemplary and explanatory only and are not restrictiveof any subject matter claimed.

In the present disclosure, the use of the singular includes the pluralunless specifically stated otherwise. It must be noted that, as used inthe specification and the appended claims, the singular forms “a,” “an”and “the” include plural referents unless the context clearly dictatesotherwise. In the present disclosure, the term “or” means “and/or”unless stated otherwise. Furthermore, use of the term “including” aswell as other forms, such as “include”, “includes,” and “included,” isnot limiting.

As used in the present disclosure, ranges and amounts are sometimesexpressed as “about” a particular value or range. About also includesthe exact amount. Hence “about 2.0” means “about 2.0” and also “2.0”.Generally, the term “about” includes an amount that would be expected tobe within experimental error. For example, the term “about” in someembodiments refers variation of ±1%, ±2%, ±3%, ±4%, ±5%, ±6%, ±7%, ±8%,±9%, or ±10%. In some embodiments, the term “about” refers to variationof ±5%. In some embodiments, the term “about” refers to variation of±10%.

As used in the present disclosure, positional relationship in someembodiments is refers to as “essentially” a particular geometricdefinition. “Essentially” also includes the exact geometric definition.Hence “essentially planar” includes “planar”, “essentially parallel”includes “parallel”, “essentially orthogonal” includes “orthogonal”, and“essentially equidistant” includes “equidistant”. Generally, the term“essentially” includes an amount that would be expected to be withinacceptable variation.

For example, the term “essentially planar” in some embodiments refers toa surface that is at least 99% planar, at least 98% planar, at least 97%planar, at least 96% planar, at least 95% planar, at least 94% planar,at least 93% planar, at least 92% planar, at least 91% planar, at least90% planar, at least 85% planar, or at least 80% planar, In someembodiments, the term “essentially planar” refers to a surface that isat least 95% planar. In some embodiments, the term “essentially planar”refers to a surface that is at least 90% planar. In some embodiments,the term “essentially planar” refers to a surface that is at least 85%planar. In some embodiments, the term “essentially planar” refers to asurface that is at least 80% planar.

Further, the term “essentially parallel” and/or the term “essentiallyorthogonal” refers to a variation of within 1°, within 2°, within 3°,within 4°, within 5°, within 6°, within 7°, within 8°, within 9°, within10°, within 11°, within 12°, within 13°, within 14°, within 15°, within20°, within 25°, or within 30°. In some embodiments, term “essentiallyparallel” and/or the term “essentially orthogonal” refers to a variationof within 5°. In some embodiments, term “essentially parallel” and/orthe term “essentially orthogonal” refers to a variation of within 10°.In some embodiments, term “essentially parallel” and/or the term“essentially orthogonal” refers to a variation of within 15°. In someembodiments, term “essentially parallel” and/or the term “essentiallyorthogonal” refers to a variation of within 20°. In some embodiments,term “essentially parallel” and/or the term “essentially orthogonal”refers to a variation of within 25°. In some embodiments, term“essentially parallel” and/or the term “essentially orthogonal” refersto a variation of within 30°.

Still further, the term “essentially equidistant” refers to a variationof an equidistant configuration that would be expected to be withinacceptable range. For example, the term “essentially equidistant” insome embodiments refers an equidistant configuration having variation of±1%, ±2%, ±3%, ±4%, ±5%, ±6%, ±7%, ±8%, ±9%, ±10%, ±15%, ±20%, or ±25%.In some embodiments, the term “about” refers to variation of ±5%. Insome embodiments, the term “about” refers to variation of ±10%. In someembodiments, the term “about” refers to variation of ±15%. In someembodiments, the term “about” refers to variation of ±20%. In someembodiments, the term “about” refers to variation of ±25%.

As used in the present disclosure, the term “conventional air pump”refers to a device or system that produces airflow withoutelectrohydrodynamic enhancement or ionic wind generation. Examples ofconventional air pumps include, but are not limited to, traditionalelectric fans, mechanical blowers, sources of vacuum, sources ofcompressed air/gas, etc.

As used in the present disclosure, the term “upstream” and “downstream”refer to positional relationships according to bulk airflow within apassageway, in which upstream is closer to the inlet of theairflow/passageway, and downstream is closer to the outlet of theairflow/passageway.

Air-to-Air Heat Exchangers

Heat exchangers are apparatuses built to provide efficient heat transferfrom one medium to another. Heat transfer generally occurs from a regionof high temperature to another region of lower temperature. In a typicalair-to-air heat exchanger, two gas streams with different temperaturesare separated by a solid wall to prevent their mixing. In operation ofair-to-air heat exchangers, heat transfer from the first gas stream(high temperature) to the second gas stream (low temperature) occurs inthree stages: (1) heat is transferred from the first gas stream to theadjacent (first) surface of the wall, (2) heat is transferred from thefirst surface to the second surface of the wall adjacent to the secondgas stream, and (3) heat is transferred from the second surface to thesecond gas stream.

During the second stage of this process, heat is generally transferredvia the solid wall by conduction, sometimes referred as heat diffusion.To achieve a high heat transfer rate, the wall material for heatexchangers is highly heat conductive (e.g. a metal) and its thickness isgenerally not significantly greater than the minimal value required forthe mechanical strength and integrity of the apparatus. As gases aregenerally poor heat conductors, heat transfer between wall surfaces andgas by conduction in stages (1) and (3) is small compared to that byforced convection, such as gas flows generated by conventional airpumps. However, the lower part of a thin gas boundary layer adjacent tothe wall surface, where the gas velocity approaches zero at the wallsurface.

One common application of air-to-air heat exchangers is in heat recoveryventilation systems, or climate chambers/air treatment chambers, such asthose associated with various enclosed spaces in a building or greenhouse. To increase the energy efficiency of heating and cooling,builders have used better construction techniques and materials togreatly reduce air leaks into and out of a building. In some buildings,this natural air infiltration now replaces inside air every 4 to 10hours, compared to every 30 minutes decades ago.

While some air tight buildings or greenhouses reduce the costs ofheating and cooling, a reduction in the outside airflow entering thebuilding sometimes lead to problems with inside air quality. Some of themost common quality issues are excess humidity, carbon dioxide, andpollutants that are produced by human habitation (cooking, cleaning,breathing, combustion, etc.), as well as the chemicals that off-gas frombuilding materials. In some hermetic greenhouses with low air changesper hour (ACH), the evapotranspiration by plants increases the relativehumidity (RH) of air to values not favorable for plant growth. Moreover,in such low ventilated greenhouses operating in warm climates and thusrequiring the cooling, solar radiation incoming to the greenhouseenclosure sometimes leads to a temperature increase above values optimalfor plant growth even if an infra-red radiation protective glass or filmis used.

In a classic heat recovery ventilation system, both the exhaust air froma compartment air-conditioned by some means and the incoming fresh airare delivered to an air-to-air heat exchanger driven by conventional airpumps, where the temperature of the warmer air decreases and thetemperature of the cooler air increases. As a result, the incoming airis pre-conditioned by the exhaust air, which leads to a reduction in thecooling or heating load on the air conditioning system and thus inenergy consumption, rather than just discharging air conditioned air outto the atmosphere. In practice, achieving higher values of temperaturetransfer efficiency requires higher values of the heat transfer area ofthe wall and the velocity of bulk air flow.

Configurations of heat exchangers disclosed herein include: (1)pipe-based, (2) cell-based, and (3) plate-based, which are schematicallyillustrated in FIGS. 1A-1C. Referring first to FIG. 1A, a pipe-basedair-to-air heat exchanger (10) includes at least one first airpassageway (12) extending between a first air inlet (14) and a first airoutlet (16), at least one second air passageway (18) extending between asecond air inlet (20) and a second air outlet (22), and at least oneheat-conductive wall (24) separating the at least one first airpassageway (12) from the at least one second air passageway (18). In thenon-limiting embodiment shown in FIG. 1A, airflow in the at least onefirst air passageway (12) is essentially orthogonal to airflow in the atleast one second air passageway (18). However, in other embodiments ofthe present disclosure (not shown), airflow in the at least one firstair passageway (12) is opposite to airflow in the at least one secondair passageway (18). The heat conductive walls (24) in the pipe-basedair-to-air heat exchanger (10) are tubular walls. In the non-limitingembodiment shown in FIG. 1A, the tubular walls have an ovalcross-sectional profile. In other embodiments, the tubular walls havecircular, rectangular, or square cross-sectional profile.

Turning now to FIG. 1B, a cell-based air-to-air heat exchanger (10)includes at least one first air passageway/cell (12) extending between afirst air inlet (14) and a first air outlet (16), at least one secondair passageway/cell (18) extending between a second air inlet (20) and asecond air outlet (22), and at least one heat-conductive wall (24)separating the at least one first air passageway (12) from the at leastone second air passageway (18). In the non-limiting embodiment shown inFIG. 1A, airflow in the at least one first air passageway/cell (12) isessentially orthogonal to airflow in the at least one second airpassageway/cell (18). However, in other embodiments of the presentdisclosure (not shown), airflow in the at least one first air passageway(12) is opposite to airflow in the at least one second air passageway(18). The heat conductive walls (24) in the cell-based air-to-air heatexchanger (10) are essentially planar, and essentially parallel walls.In the non-limiting embodiment shown in FIG. 1A, the heat conductivewalls (24) are essentially equidistantly arranged. In other embodiment,the essentially planar walls have varying wall-to-wall distances. In theembodiment shown in FIG. 1B, the air passageways/cells have a triangularcross-sectional profile. In other embodiments, the air passageways/cellshave rectangular or square cross-sectional profile.

Referring now to FIG. 1C, a plate-based air-to-air heat exchanger (10)includes at least one first air passageway (12) extending between afirst air inlet (14) and a first air outlet (16), at least one secondair passageway (18) extending between a second air inlet (20) and asecond air outlet (22), and at least one heat-conductive wall (24)separating the at least one first air passageway (12) from the at leastone second air passageway (18). In the non-limiting embodiment shown inFIG. 1A, airflow in the at least one first air passageway (12) isessentially orthogonal to airflow in the at least one second airpassageway (18). However, in other embodiments of the present disclosure(not shown), airflow in the at least one first air passageway (12) isopposite to airflow in the at least one second air passageway (18). Theheat conductive walls (24) in the cell-based air-to-air heat exchanger(10) are essentially planar, and essentially parallel walls. In thenon-limiting embodiment shown in FIG. 1A, the heat conductive walls (24)are essentially equidistantly arranged. In other embodiment, the heatconductive walls (24) have varying wall-to-wall distances.

Electrohydrodynamic Device

Ionic wind, also known as ion wind, corona wind, coronal wind, electricwind and electrohydrodynamic (EHD) wind, is the localized air flowinduced by electrostatic forces linked to corona discharge arising atthe external surface of an electrode with relatively “sharp” surfacefeatures, i.e. surface areas of relatively low radius of curvatures onwhich corona discharge occurs, which is generally referred to as theemitter electrode in the present disclosure. The relatively “sharp”surface features include, but are not limited to, needles, wedges, tips,edges, threads, spiks, barbs, blades, etc. In some embodiments, theradium curvature of the relatively “sharp” surface features on theemitter electrode approaches zero, such as for example needles andblades.

In use, the emitter electrode is at a high voltage relative to anotherelectrode with relatively “blunt” surface features, i.e. surface areasof relatively high radius of curvatures on which corona discharge doesnot occur, which is generally referred to as the enhancer electrode andcollector electrode in the present disclosure. The relatively “blunt”surface features include, but are not limited to, flat surfaces, smoothcylindrical surfaces or sections thereof, smooth spherical surfaces orsections thereof, etc. In some embodiments, the radium curvature of therelatively “blunt” surface features on the emitter electrode approachesinfinity, such as for example flat surfaces.

Referring now to FIG. 2, a basic EHD device 40 is illustrated as havingone or more emitter electrodes (42) and one or more collector electrodes(46) positioned downstream of the one or more emitter electrodes (42).In the pipe-based embodiment shown in FIG. 2A, the one or more emitterelectrodes (42) and the one or more collector electrodes (46) extend ina direction essentially orthogonal to the airflow. An electric potentialdifferential is created between the emitter electrodes (42) and thecollector electrodes (46). In the non-limiting embodiment shown in FIG.2A, the emitter electrodes (42) are connected to a source of positiveelectric potential and the collector electrodes (46) are grounded. Inother embodiments (not shown), the emitter electrodes (42) are connectedto a source of positive electric potential and the collector electrodes(46) are connected to a source of negative electric potential.

Electric charges on electrodes generally reside on their externalsurfaces, which results in high strengths of electric field in thevicinity of their external surfaces. If this electric field strengthexceeds a threshold value, known as the gradient of corona dischargeinception potential, some air molecules are ionized through electronattachment or detachment in an area around the external surface ofemitter electrodes (42). This area is referred to as the ionization zone(43).

Most of ionized air molecules produced by corona discharge have the sameelectric sign as that of the emitter electrodes (42). Withinmilliseconds after its ionization, i.e. loosing or gaining the electron,an air molecule attracts electrically polar air molecules (i.e.possessing the own electrical dipole moment) of water and some tracegases, which leads to the formation of a small charged molecular clusterthat is called air ion. Air ions are repulsed from the like-chargedemitter electrode (42), leave the ionization zone (43), and then drifttowards the collector electrode (46), driven by the electric force inthe electric field between the emitter electrodes and the collectorelectrodes, and the electric field of the air ion space charge. Asillustrated in FIG. 2A, ionic wind is produced by the momentum transferfrom the moving air ions to air molecules that collide with air ions,which enhances airflow within the air passageways.

In the electrohydrodynamic (EHD) device, the electric energy is directlyconverted to the energy of bulk air motion. This is in contrast to theprocess in a conventional air pump, such as for example an electric fan,in which electric energy is first converted to the kinetic energy of thefan and then to the energy of bulk air motion. The ion-driven airpropulsion is achieved without moving mechanical parts. In someembodiments, the ion-driven air propulsion is controlled by the voltageof corona discharge. The present disclosure recognizes that awell-designed EHD device is more energy efficient and/or has betterperformance than electric fans and other conventional air pumps.

Generally, the operating voltage range for corona discharge lies betweenthe corona onset voltage and breakdown voltage of air gap betweenemitter and collector electrodes. In practice, the highest acceptablevoltage is in some cases smaller and determined by ozone productionconstraints. Ion wind is produced with positive, negative, or evenalternate electrical polarity of emitter electrodes. Due to a slightlylower electrical mobility of positive air ions compared to that ofnegative ones, a higher ion wind velocity is sometimes achieved bypositive corona discharge. The present disclosure recognizes thatperformance of EHD devices in air-to-air heat exchangers depends onfactors including, but not limited to, the electric potential of theelectrodes, position and configuration of the electrodes, devicegeometry, etc.

In addition, the present disclosure recognizes that the short-rangenature of ionic wind is sometimes improved by using a plurality of EHDdevices operating in sequence. Referring to FIG. 2B, two EHD devices(40, 40′) are illustrated as operating in sequence. The upstream EHDdevice 40 is illustrated as having one or more emitter electrodes (42)and one or more collector electrodes (46) positioned downstream of theone or more emitter electrodes (42). The downstream EHD device (40′) isillustrated as having one or more emitter electrodes (42′) positioneddownstream of the one or more collector electrodes (46) of the upstreamEHD device, and one or more collector electrodes (46′) positioneddownstream of the one or more emitter electrodes (42′).

In the embodiment shown in FIG. 2B, the one or more emitter electrodes(42, 42′) and the one or more collector electrodes (46, 46′) extend in adirection essentially orthogonal to the airflow. An electric potentialdifferential is created between the emitter electrodes (42) and thecollector electrodes (46), and between the emitter electrodes (42′) andthe collector electrodes (46′). In the non-limiting embodiment shown inFIG. 2B, the emitter electrodes (42, 42′) are connected to a source ofpositive electric potential and the collector electrodes (46, 46′) aregrounded.

Enhancer Electrode

In some embodiments, the efficiency of EHD devices is increased byutilizing an enhancer electrode to refine the electric field and thusfurther enhance the range/velocity of the ionic wind. The enhancerelectrode has an electric potential between the electric potential ofthe emitter electrode and the electric potential of the collectorelectrode, and as such serves to partially de-couple ionization and iondrift. Referring now to FIG. 3, a three-electrode EHD device (40) isillustrated as having one or more emitter electrode (42), one or moreenhancer electrodes (44), and one or more collector electrodes (46). Theone or more emitter electrodes (42), the one or more enhancer electrode(44), and the one or more collector electrodes (46) extend in adirection essentially orthogonal to the airflow. The enhancer electrode(44) is positioned downstream of the emitter electrodes (42) andupstream of the collector electrode (46). In the non-limiting embodimentshown in FIG. 3, the enhancer electrode (44) is closer in proximity tothe emitter electrode (42) than the collector electrode (46).

In operation, ions created in the vicinity of the emitter electrode (42)drift towards the enhancer electrode (44); but instead of all ions beingcollected there, some ions continue to drift towards the collectorelectrode (46) due to a potential difference between the enhancerelectrode (44) and the collector electrode (46). As a result, thedistance traveled by the ions is increased without significant effect onthe corona characteristics. In such a configuration, the overall ioniccurrent from the discharge and the achieved air flow rate issignificantly increased without altering the standard corona dischargeto the primary collecting electrode.

Still referring to FIG. 3, in some embodiments where the ionic windflows essentially parallel to the heat conductive dielectric wall (24),the enhancer electrode (44) is covered by an optional insulatingdielectric barrier (45). It is contemplated that the insulatingdielectric barrier (45) reduces the ion loss on the enhancer electrode(44). In some embodiments, the voltage of the enhancer electrode has aduty cycle, in which this voltage periodically matches the voltage ofthe emitter electrode (42). At the latter condition, the chargeaccumulated on the surface of dielectric barrier will be driven off andaccelerated towards the collector electrode (46). Such intermittentdischarges reduce the maximum charge accumulated on the barrierinsulating dielectric barrier (45). The present disclosure recognizesthat uncontrolled increase in this charge would result in eitherelectrical breakdown of the dielectric barrier (45) or a decrease in thepotential between the emitter electrode (42) and the enhancer electrode(44), which ultimately leads to termination of corona discharge.

In the embodiment shown in FIG. 3, the emitter electrode (42) iselectrically coupled to the positive electrode of the first high voltagedirect current (HVDC) source, the second electrode of which is grounded.The enhancer electrode (44) is grounded. The collector electrode (46) iselectrically coupled to the negative electrode of the second HVDCsource, the second electrode of which is grounded.

The present disclosure recognizes that the efficiency of ionacceleration on the second stage is higher, sometimes much higher, thanthat efficiency on the first stage, and as a result the overallefficiency of the EHD device having emitter-enhancer-collectorelectrodes (i.e. emitter-enhancer-collector EHD device) is highercompared to that of a reference EHD device having emitter-collectorelectrodes without the enhancer electrode (i.e. emitter-collector EHDdevice). In some embodiments, the energy consumption of theemitter-enhancer-collector EHD device is lower than that of theemitter-collector EHD device for the same exit flow velocity. In someembodiments, the thrust achieved by the emitter-enhancer-collector EHDdevice is higher than that of the emitter-collector EHD device for thesame energy consumption. In some optimized setup, theemitter-enhancer-collector EHD device achieves both lower energyconsumption and higher thrust compared to the emitter-collector EHDdevice.

The present disclosure recognizes the importance of efficientionization, i.e. reducing ion loss, in particular on the enhancerelectrode, for further enhancing airflow velocity and energy efficiency.In addition to the introduction of dielectric barriers to enhancerelectrodes with variable potential as previously discussed, anotherfeature contemplated in the present disclosure is the production ofpulsed corona discharges repetitively to allow air ions produced duringthe pulse of voltage on the emitter electrode to be diverted to thecollector electrode before reaching the enhancer electrode on which theyrecombine.

Pipe-Based Heat Exchangers Using Emitter-Enhancer-Collector EHDEnhancement

In some embodiments, the EHD devices disclosed herein, such as thoseusing annular electrodes (e.g. shown in FIG. 2A), is incorporated intothe pipe-based air-to-air heat exchanger, provided that the dielectricmaterial of pipes or square ducts has high heat conductivity. Suchmaterials, that are typically plastics with the inclusion of multi-sizedparticles of alumina (Al2O3) or a number of other suitable substances,are available in mass production. The bulk air propulsion achieved inthe EHD devices is due to ionic wind jets produced in the vicinity ofthe internal surface of pipe or square duct. Additionally, those jetscause a significant increase in the coefficient of air-to-wall(convective) heat transfer. The latter increase is due to asignificantly higher disturbance of boundary layer of air near theinternal surface of pipe or duct in the enhanced air velocity profile(i.e. that after passing the ionic air propulsion generator) compared tothat disturbance by the bulk air flow. The visual comparison of velocityprofiles of bulk and enhanced air flows, i.e. those before and after thesaid generator is illustrated in the top diagram of FIG. 2A.

In the EHD enhanced pipe-based or duct-based air-to-air heat exchanger,the bulk air flow produced by EHD devices operating in sequence reduces,if not eliminates, the need for a conventional air pump, such as atraditional electric fan. Additionally, the heat transfer exchangebetween that air flow and the wall separating two air flows is sometimessignificantly enhanced due to an increase in the coefficient ofair-to-wall heat transfer, which ultimately leads to an increase intemperature transfer efficiency of the heat exchanger.

Referring now to FIG. 4A, a duct-based air-to-air heat exchanger (10)includes a dielectric heat conductive wall (24) having a square orrectangular cross-sectional profile, one or more emitter electrode (42),one or more enhancer electrode (44), and one or more collector electrode(46). Both the enhancer electrodes (44) and the collector electrodes(46) are in the shape of flat strips and with smooth edges to preventparasitic corona discharge, arranged essentially orthogonal to the airflow direction and attached to internal surfaces of the duct walls (24).In some embodiments, the length of the enhancer electrodes (44) and thecollector electrodes (46) are the same as the width of the wall surfacesto which the electrodes attach. The enhancer electrodes (44) and thecollector electrodes (46) are mechanically secure to the heat conductivewall (24), and thermally coupled to the heat conductive wall (24), e.g.providing a layer of a highly heat conductive medium between electrodesand walls.

Turning to FIG. 4B, the second configuration of the duct-basedair-to-air heat exchanger (10) differs from the first configurationillustrated in FIG. 4A by deploying two electrically coupled emitterelectrodes (42). The feature of this modified configuration is a lowercorona onset voltage. It is contemplated that the lower onset voltage isattributable to the symmetrical (relative to each of two emitterelectrode of corona discharge) presence of the electric charge, theemitter electrode and space charge produced (in this case theintermediate enhancer electrode is responsible for corona onset).

Referring now to FIG. 5, a pipe-based air-to-air heat exchanger (10)includes a dielectric heat conductive wall (24) having a circular oroval cross-sectional profile, one or more emitter electrode (42), one ormore enhancer electrode (44), and one or more collector electrode (46).In this embodiment, the emitter electrode (42) is in the shape of needlelocated at the axis of the pipe (dielectric support is not shown) withits sharp tip pointing to a downstream direction. Both the enhancerelectrodes (44) and the collector electrodes (46) are in the shape ofloops of electrically conductive strips. The enhancer electrodes (44)and the collector electrodes (46) are mechanically secure and thermallycoupled to the internal surface of pipe in the same way as previouslydiscussed in connection with the embodiments shown in FIGS. 4A and 4B.

Plate-Based Heat Exchangers Using Emitter-Enhancer-Collector EHDEnhancement

In some embodiments of the plate-based heat exchangers according to thepresent disclosure, it is contemplated herein that possible vaporcondensation on one surface of heat conductive walls separating airflowsof different temperatures would make the wall surface electricallyconductive. To operate in electrically conductive enclosure, someembodiments of plate-based heat exchangers use a plurality ofemitter-enhancer-collector EHD devices operating in sequence.

One feature of the plate-based heat exchanger comprising a plurality ofemitter-enhancer-collector EHD devices operating in sequence is theenhancement of the overall performance of the heat exchanger by theintroduction of ion wind generators in the second airflow leading to theenhancement of heat transfer on the other surface of air flow separatingwall. This would reduce, if not eliminate, the need for conventional airpumps and lead to an enhancement of convective heat transfer coefficientbetween the wall and the second airflow. This brings the feature ofminimizing the electric field interference between the neighboring ionicwind generation engines that sometimes lead to their performancedegradation. Therefore, in a preferred embodiment, the collection ofcorona electrodes of a particular ionic wind generator should bearranged at the maximum possible distance from the neighboringgenerators. This brings the feature that the directions of heatexchanging airflows in the proposed heat exchanger are opposite, whichleads to the feature that ionic wind generator electrodes as whole indifferent airflow channels are essentially parallel to each other andshifted by a distance which is the half of the distance between them inthe neighboring flow channel. Schematic configuration of thisarrangement is presented in FIG. 6.

In the embodiment shown in FIG. 6, each emitter-enhancer-collector EHDdevice (40) includes one or more emitter electrodes (42) in the form ofone or more elongated members, one or more enhancer electrodes (44) inthe form of one or more elongated members, which are electricallycoupled to electrically conductive and grounded heat exchanger plates,and one or more collector electrodes (46) in the form of one or moreelongated members, or smooth-edged electrically conductive strips, whichare at an electrical potential relative to the ground with the signopposite to that of emitter electrode.

In some embodiments, the enhancer electrodes (44) of the EHD devices(40) are electrically coupled and grounded. The emitter electrodes (42)of the EHD devices (40) are electrically coupled to each other and tothe positive (in this example) electrode of the first HVDC source, whichnegative electrode is earthed. The collector electrodes (46) of the EHDdeices (40) are electrically coupled to each other and to the negative(in this example) electrode of the second HVDC source, which positiveelectrode is earthed. In some embodiments, direct current of a certainpolarity supplied to the one or more emitter electrodes is provided inperiodic pulses.

Plate-Based Heat Exchangers with Electrically Conductive Walls

Sometimes, atmosphere air entering a heat exchanger has high relativehumidity, which leads to condensation walls of the heat exchanger.Designs of commercial heat exchangers typically include the means forcollecting and discarding the condensed water. This includes thepreferably vertical position of heat exchanger walls such as pipes,cells, or plates, a tray for collecting water drops descending from thewalls, and an outlet that allow this water to leave the heat exchanger.As the water condensed on the surface of heat exchanger wall makes itelectrically conductive, EHD devices of some embodiments of the presentdisclosure are configured to work under this condition regardless onwhich side of the wall the condensation occurred. In such embodiments,EHD devices are configured for heat exchanger walls that are made ofthermally conductive and electrically conductive materials, such ascertain metals as non-limiting examples.

Referring to FIG. 7A, the emitter-enhancer-collector EHD device (40)includes one or more emitter electrodes (42) in the form of one or moreelongated members, one or more enhancer electrodes (44) in the form ofone or more elongated members, which are electrically coupled toelectrically conductive and grounded heat exchanger plates, and one ormore collector electrodes (46) in the form of one or more elongatedmembers, or smooth-edged electrically conductive strips, which are at anelectrical potential relative to the ground with the sign opposite tothat of emitter electrode.

The emitter electrode (42), the enhancer electrodes (44) and thecollector electrodes (46) are separated from their closest heatconductive wall (24) by predetermined distances. For example, theemitter electrode (42) is separated from the closest wall (24) by anemitter-wall distance. The enhancer electrodes (44) are separated fromthe closest wall (24) by an enhancer-wall distance. The collectorelectrodes (46) are separated from the closest wall (24) by acollector-wall distance. In some embodiment, such as the embodimentshown in FIG. 7A, the collector-wall distance is less than theenhancer-wall distance. In some embodiments, the enhancer-wall distanceis less than the emitter-wall distance. In some embodiments, thecollector-wall distance is less than the enhancer-wall distance, whichin turn is less than the emitter-wall distance. It is contemplated thatsuch positional configurations contribute to the improvement of windvelocity near the wall. In addition, the present disclosure recognizesthat the collector-wall distance should have a minimum threshold aspositioning the collector electrode (46) too close to the heatconductive wall (24) sometimes decreases the performance and/orefficiency of the EHD devices, such as requiring a higher voltage tooperate. It is contemplated in the present disclosure that acollector-wall distance too small would lead to the effective electricfield of the collector electrode being close to a dipole of oppositecharge lines, requiring a significantly higher voltage of the connectedpower source would be required.

In some embodiments, the enhancer electrodes (44) of the EHD devices(40) are electrically coupled and grounded. The emitter electrodes (42)of the EHD devices (40) are electrically coupled to each other and tothe positive (in this example) electrode of the first HVDC source, whichnegative electrode is earthed. The collector electrodes (46) of the EHDdeices (40) are electrically coupled to each other and to the negative(in this example) electrode of the second HVDC source, which positiveelectrode is earthed. In some embodiments, direct current of a certainpolarity supplied to the one or more emitter electrodes is provided inperiodic pulses.

Turning to FIG. 7B, the second configuration of the plate-basedair-to-air heat exchanger (10) differs from the first configurationillustrated in FIG. 7A by deploying two electrically coupled emitterelectrodes (42). The feature of this modified configuration is a lowercorona onset voltage. It is contemplated that the lower onset voltage isattributable to the symmetrical (relative to each of two emitterelectrode of corona discharge) presence of the electric charge, theemitter electrode and the space charge produced (in this case theintermediate enhancer electrode responsible for corona onset).

In addition, similar to the configuration of the EHD-enhanced plate-baseexchanger shown in FIG. 6, where multiple EHD devices operate insequence in both air passageways divided by non-conductive plates,multiple EHD devices shown in FIGS. 7A and 7B are also configured insequence in one or both of first and second air passageways divided byelectrically conductive plates in some embodiments of the presentdisclosure.

Convection Promoter Electrodes

In some embodiments, the EHD devices shown in FIGS. 7A and 7B havingionic wind velocity profile that is close to that of bulk air, i.e. theionic wind velocity in the vicinity of wall is lower than that achievedin the bulk air. This is because the air acceleration by ion drag in theelectric field of collector electrode continues only up to the collectorelectrode, a feature of EHD devices operating in an electricallyconductive enclosure. A lower wind velocity in the vicinity of the wallleads to a lower coefficient of convective heat transfer. While usingEHD devices operating in sequences between the electrically conductiveplates of heat exchanger would result in a fully EHD-driven embodimentwithout conventional air pumps, the overall performance and efficiencyof the heat exchangers in some embodiments are further enhanced throughimprovement of heat transfer feature.

In some embodiments, such improvement is achieved by introducing anarray of electrodes in the vicinity of each surface of each wall toproduce short-range ionic wind in the vicinity of the wall surface,which de-couples the EHD production of bulk airflow for the enhancementof the convective heat transfer coefficient. This feature allows controlof the bulk airflow, which velocity is determined by a certainoperational regime in a particular application, while enhancing the heatexchange efficiency with short-rage ionic wind independently. Thearrangement and configuration of EHD devices that further incorporateconvection promoter electrode to generate short-range ionic wind isshown in FIGS. 8 and 9.

In FIG. 8, an EHD device (40) is illustrated as having one or moreemitter electrodes (42), one or more enhancer electrodes (44), one ormore collector electrodes (46), and one or more arrays of convectionpromoter electrodes (50). In some embodiments, the enhancer electrodes(44) of the EHD devices (40) are electrically coupled to the wall (24)and grounded. The emitter electrodes (42) of the EHD devices (40) areelectrically coupled to each other and to the positive (in this example)electrode of the first HVDC source, which negative electrode is earthed.The collector electrodes (46) of the EHD deices (40) are electricallycoupled to each other and to the negative (in this example) electrode ofthe second HVDC source, which positive electrode is earthed. Theconvection promoter electrodes (50) are electrically coupled to thepositive electrode of the first HVDC source, or the negative electrodeof the second HVDC, or the positive or negative electrode of a separatethird HVDC source. In some embodiments, direct current of a certainpolarity supplied to the one or more emitter electrodes is provided inperiodic pulses.

In some embodiments, the emitter electrode (42), the enhancer electrodes(44), the collector electrodes (46), and the convection promoterelectrodes are separated from their closest wall (24) by predetermineddistances. For example, the emitter electrode (42) is separated from theclosest wall (24) by an emitter-wall distance. The enhancer electrodes(44) are separated from the closest wall (24) by an enhancer-walldistance. The collector electrodes (46) are separated from the closestwall (24) by a collector-wall distance. The convection promoterelectrodes (50) are separated from the closest wall (24) by apromoter-wall distance (h). In some embodiment, such as the embodimentshown in FIG. 8, the promoter-wall distance (h) is less than any of theemitter-wall distance, the enhancer-wall distance, and thecollector-wall distance. In some embodiments, such as the embodimentshown in FIG. 8, the array of convection promoter electrodes isessentially equidistantly arranged in the direction of airflow, with aseparation distance between the neighboring emitter electrodes,hereinafter referred to as promoter-promoter distance (s).

In some embodiments, the promoter-promoter distance (s) is greater thanthe promoter-wall distance (h). In some embodiments, thepromoter-promoter distance (s) is not less than two times thepromoter-wall distance (h). In some embodiments, the promoter-promoterdistance (s) is not less than three times the promoter-wall distance(h).

In some embodiments, such as the embodiment shown in FIG. 8, two arraysof convection promoter electrodes (50) are provided in the airpassageway between two adjacent walls, and have the same electricpotential, such as by coupling to the same positive or negativeelectrode of a HVDC source. In some embodiments, an array of convectionpromoter electrode (50) in a first air passageway and an array ofconvection promoter electrodes (50) in a second air passageway arepositioned at opposite sides of the same wall (24) dividing the firstand second air passageways. In some embodiments, the two arrays ofconvection promoter electrodes (50) separated by the wall (24) haveelectric potential of opposite polarities, such as by coupling one arrayof the convection promoter electrodes (50) to a position or negativeelectrode of a HVDC source and coupling the other array of convectionpromoter electrodes (50) to the other electrode of the HVDC source. Insome embodiments, the two arrays of convection promoter electrodes (50)separated by the wall (24) have the same promoter-wall distance but areoffset in a direction of airflow by an offset distance (u).

In some embodiments, the offset distance (u) between two arrays ofconvection promoter electrodes (50) at opposite sides of a particularwall (and therefore of opposite electric signs) is dependent on thedirection of bulk air flow in a particular air passageway. It iscontemplated that this feature ensures that the tangential (relative tothe surface of wall) component of electrical force on the produced ionsthat tends to be directed to the closest convection promoter electrodeof corona discharge of the opposite charge across the wall is in thesame direction as the bulk airflow in each channel, and as such theadditional airflow caused by the short-range ionic wind is in the samegeneral direction as the bulk airflow. The normal (relative to thesurface of wall) component of electrical force on the produced ionsdirected towards the wall ensures that the additional air flow producedby the described short-range ionic wind generators is kept in thevicinity of the wall surface. On the microscopic level, the additionaleffect of the said component of electric force is to drag the air fromareas with different temperatures along the trajectory of an ionapproaching the wall through the low-velocity boundary layer in thevicinity of the wall.

In some embodiments, the promoter-promoter distance (s) in each array isno less than a minimum distance that is two times the promoter-walldistance plus the offset distance (2h+u). In some embodiment, thepromoter-promoter distance (s) in each array is no more than a maximumdistance that is X times the minimum distance described above, i.e.X(2h+u). In some embodiment, the parameter X ranges between about 1.1and about 5.0. In some embodiment, the parameter X ranges between about1.1 and about 5.0. In some embodiment, the parameter X ranges betweenabout 1.1 and about 4.0. In some embodiment, the parameter X rangesbetween about 1.1 and about 3.0. In some embodiment, the parameter Xranges between about 1.1 and about 2.0. In some embodiment, theparameter X ranges between about 1.5 and about 2.0. In some embodiment,the parameter X is about 1.1, about 1.2, about 1.3, about 1.4, about1.5, about 1.6, about 1.7, about 1.8, about 1.9, about 2.0, about 2.5,or about 3.0. It is contemplated that the combination of the electrical,positional and/or geometric configurations of the convection promoterelectrodes (50), or with further combination with electrical, positionaland/or geometric configurations of the emitter electrodes (42), theenhancer electrodes (44), and collector electrodes (46) contribute toimproved bulk airflow and surface airflow, as well as overallimprovement of performance and efficiency of the heat exchangers.

Referring now to FIG. 9, the present disclosure recognizes that furtherimprovement to the heat exchangers incorporating both bulk andshort-range ion wind generators in the plate-based heat exchangercomprising electrically conductive plates is achieved by the selectionand configurations of the corona sign, e.g. the electrical sign of theemitter electrodes (42) and the convection promoter electrodes (50). Anon-limiting example is provided in FIG. 9.

In FIG. 9, the air passageways separated by the heat conductive wall 24are each configured with EHD devices (40) operating in sequence. The EHDdevices (40) within each air passageway have the same corona sign, i.e.either positive corona or negative corona. The EHD devices (40) in twoneighboring air passageways have opposite corona sign, i.e. the EHDdevices (40) in one air passageway have positive corona sign and the EHDdevices (40) in the neighboring air passageway have negative coronasign, or vice versa. The present disclosure recognizes that thealternate signs of emitter electrodes of corona discharge in someembodiments reduces or minimizes the corona inception voltage. In someapplications, EHD devices (40) (e.g. bulk ionic wind generators) withpositive corona are used in the passageway of exhaust airflow, and EHDdevices (40) (e.g. bulk ionic wind generators) with negative corona areused in the passageway of incoming airflow. It is recognized that thisconfiguration allows s some negative ions to be present in the airflowinto the building (e.g a greenhouse or a residential or commercialbuilding), which has beneficial effects (e.g. health effects) on plants,humans, and animals.

In some non-limiting embodiments, the EHD device (40) have convectionpromoter electrode (50) positioned both upstream and downstream of theEHD device (40). In some embodiments, the upstream convection promoterelectrodes (50) have the same corona sign as the EHD device (40) whilethe downstream convection promoter electrode (50) have the oppositecorona sign as the EHD device (40). In some embodiments, such as theembodiment shown in FIG. 9, two arrays of convection promoter electrodes(50) are provided in the air passageway between two adjacent walls, andhave the same electric potential, such as by coupling to the samepositive or negative electrode of a HVDC source. In some embodiments, anarray of convection promoter electrode (50) in one air passageway and anarray of convection promoter electrodes (50) in another neighboring airpassageway are positioned at opposite sides of the same wall (24)dividing the first and second air passageways. In some embodiments, thetwo arrays of convection promoter electrodes (50) separated by the wall(24) have electric potential of opposite polarities, such as by couplingone array of the convection promoter electrodes (50) to a position ornegative electrode of a HVDC source and coupling the other array ofconvection promoter electrodes (50) to the other electrode of the HVDCsource. In some embodiments, the two arrays of convection promoterelectrodes (50) separated by the wall (24) have the same promoter-walldistance but are offset in a direction of airflow by an offset distance(u), such as those describe in embodiments shown in FIG. 8.

Application and Usage

The present disclosure recognizes that the EHD enhanced air-to-air heatexchanger in some embodiments are suitable for use in essentiallyenclosed spaces, such as spaces that are generally enclosed except fornecessary practical or operational purposes including, but not limitedto, space entry, space exit, convenience and recreation, safetyprotocols and regulations, construction/manufacturing protocols andregulations, etc. For non-limiting examples, the essentially enclosedspace includes, but is not limited to, space in: (1) residentialbuildings and school buildings, (2) commercial buildings (including forexample shopping malls, hotels, restaurants, office buildings,hospitals, airports, data centers, arenas, stadiums, etc.); (3)industrial/manufacturing buildings (e.g. assembly line factories, powerstations, etc.); (4) horticultural buildings or enclosures (e.g.greenhouses, etc.); (5) underground networks (e.g. underground mines,subways or underground metro systems, underground residential or officeestablishments etc.).

Generally, the practical limitation to the voltages of emitterelectrodes of corona discharge is related to the concentration ofcorona-generated ozone in the conditioned air, which acceptable leveldepends on a particular application, such as in residential buildings orin commercial establishments including for example airports, datacenters, arenas, stadiums, etc. The present disclosure recognizes thatfor using EHD air-to-air heat exchangers in greenhouses, this limitationis relaxed compared to because it was found that ozone at a certainlevel/amount is beneficial for plant growth.

In some embodiments, heat exchangers according to the present disclosurefurther include an insulating enclosure housing for the plates of heatexchanger and/or insulating supports for all electrodes. In someembodiments, the enclosure housing also includes collection tray and anoutlet for the condensed water. As a non-limiting example, the condensedwater harvested from an EHD air-to-air heat exchanger in an air coolingsystem for a greenhouse operating in a warm and humid environmentsignificantly reduces the total water consumption from an externalsource, e.g. water desalination system in arid areas.

The foregoing is illustrative of the present disclosure, and is not tobe construed as limiting thereof. While embodiments of the presentdisclosure have been indicated and described herein, it will be obviousto those skilled in the art that such embodiments are provided by way ofexample only. Numerous variations, changes, and substitutions will nowoccur to those skilled in the art without departing from the presentdisclosure. It should be understood that various alternatives to theembodiments of the present disclosure are within the scope of thepresent disclosure.

1. An air-to-air heat exchanger, comprising: at least one first airpassageway extending between a first air inlet and a first air outlet;at least one second air passageway extending between a second air inletand a second air outlet; at least one heat-conductive wall separatingthe at least one first air passageway from the at least one second airpassageway; and at least one electrohydrodynamic device disposed in atleast one of the first and second air passageways for enhancing airflowtherein, wherein each electrohydrodynamic device comprises one or moreemitter electrodes, one or more enhancer electrodes positioneddownstream of the one or more emitter electrodes, and one or morecollector electrodes positioned downstream of the one or more enhancerelectrodes.
 2. The heat exchanger of claim 1, wherein the at least oneheat conductive wall comprises at least one essentially planar wall. 3.The heat exchanger of claim 1, wherein the at least one heat conductivewall comprises a plurality of essentially planar walls that areessentially parallel to one another.
 4. The heat exchanger of claim 3,wherein the plurality of heat conductive walls are essentiallyequidistantly arranged.
 5. The heat exchanger of claim 3, whereinairflow in the first air passageway and airflow in the second airpassageway are essentially in opposite direction.
 6. (canceled)
 7. Theheat exchanger of claim 1, wherein the one or more emitter electrodes,the one or more enhancer electrodes, and the one or more collectorelectrodes extend essentially parallel to heat conductive walls andessentially orthogonal to the airflow.
 8. The heat exchanger of claim 7,wherein the one or more emitter electrodes have a higher electricpotential than the one or more enhancer electrodes, and wherein the oneor more enhancer electrodes have a higher electric potential that theone or more collector electrode.
 9. The heat exchanger of claim 8,wherein the one or more enhancer electrodes are grounded.
 10. The heatexchanger of claim 9, wherein the one or more enhancer electrodes arepositioned closer to the one or more emitter electrode than to the oneor more collector electrodes.
 11. The heat exchanger of claim 10,wherein the one or more emitter electrodes are separated from theclosest heat conductive wall by an emitter-wall distance.
 12. The heatexchanger of claim 11, wherein the one or more enhancer electrodes andthe one or more collector electrodes are attached to the heat conductivewall, and wherein the heat conductive wall is dielectric.
 13. The heatexchanger of claim 12, wherein the one or more enhancer electrodes andthe one or more collector electrodes are made of heat conductivematerial.
 14. The heat exchanger of claim 11, wherein the heatconductive wall is electrically conductive and grounded, wherein the oneor more enhancer electrodes are separated from the closest heatconductive wall by an enhancer-wall distance, and wherein the one ormore collector electrodes are separated from the closest heat conductivewall by a collector-wall distance.
 15. The heat exchanger of claim 14,wherein the collector-wall distance is smaller than the enhancer-walldistance.
 16. The heat exchanger of claim 15, wherein the collector-walldistance and the enhancer-wall distance are both smaller than theemitter-wall distance.
 17. The heat exchanger of claim 14, wherein eachelectrohydrodynamic device further comprises one or more arrays ofconvection promoter electrodes positioned downstream of the one or morecollector electrodes.
 18. The heat exchanger of claim 17, wherein one ormore arrays of convection promoter electrodes extend essentiallyparallel to the heat conductive walls and essentially orthogonal to theairflow.
 19. The heat exchanger of claim 18, wherein the convectionpromoter electrodes are separated from the closest heat conductive wallby a promoter-wall distance of (h) that is smaller than any of theemitter-wall distance, enhancer-wall distance, and collector-walldistance.
 20. The heat exchanger of claim 19, wherein the convectionpromoter electrodes within each array are separated from one another bya promoter-promoter distance (s) that is greater than the promoter-walldistance (h).
 21. The heat exchanger of claim 20, wherein eachelectrohydrodynamic device comprises two array of the convectionpromoter electrodes positioned between two adjacent heat conductivewalls, wherein both arrays and have same electrical potential.
 22. Theheat exchanger of claim 21, wherein one array of convection promoterelectrodes of a first electrohydrodynamic device and one array ofconvection promoter electrodes of a second electrohydrodynamic deviceare disposed on opposite side of a heat conductive wall with an offsetdistance (u), and have opposite electric potentials.
 23. The heatexchanger of claim 22, wherein the promoter-promoter distance (s) is noless than 2h+u, and wherein the promoter-promoter distance (s) is nogreater than X(2h+u), wherein X ranges between 1.5 and 2.0.
 24. The heatexchanger of claim 1, wherein the at least one first air passageway, theat least one second air passageway, the at least one heat-conductivewall, and the at least one electrohydrodynamic device are enclosed in ahousing.
 25. The heat exchanger of claim 24, wherein the housingcomprises the first air inlet, the first air outlet, the second airinlet, and the second air outlet.
 26. A ventilation system comprising adesiccator and the heat exchanger of claim 25, wherein the first airinlet of the heat exchanger is configured to receive air fromatmosphere, the first air outlet of the heat exchanger is connected tothe desiccator.
 27. The ventilation system of claim 26, wherein thesecond air inlet of the heat exchanger is configured to receive exhaustair from the ventilation system, and wherein the second air outlet ofthe heat exchanger is configured to release air into atmosphere.
 28. Theventilation system of claim 26, wherein a temperature of air enteringinto the first air inlet of the heat exchanger is higher than atemperature of air exiting the second air outlet of the heat exchanger.29. A method of enhancing air flow in an air-to-air heat exchanger, themethod comprising: activating at least one electrohydrodynamic devicedisposed in air passageways of the air-to-air heat exchanger, whereineach electrohydrodynamic device comprises one or more emitterelectrodes, one or more enhancer electrodes positioned downstream of theone or more emitter electrodes, and one or more collector electrodespositioned downstream of the one or more enhancer electrodes, whereinthe activation comprises creating gradient electric potentialdifferential from the emitter electrodes to the enhancer electrodes andto the collector electrodes.
 30. The method of claim 1, wherein theactivation comprises coupling the emitter electrodes with a source ofpositive electric potential, coupling the collector electrode with asource of negative electric potential, and grounding the enhancerelectrodes.